Waspaloy (UNS N07001) is a precipitation hardenable, nickel-base alloy which is used in elevated temperature applications. The alloy has found particular utility in gas turbine engine parts and aircraft jet engines that require considerable strength and good resistance to oxidation and hot corrosion at temperatures up to about 1600° F. (871° C.). Waspaloy provides good resistance to hot corrosion that results from exposure to combustion byproducts encountered in gas turbines and aircraft jet engines. A disadvantage of Waspaloy is that it is a relatively expensive alloy compared to other nickel-base superalloys. The higher cost of Waspaloy is attributable to the high amounts of nickel and cobalt used in the alloy and the difficulty of processing the alloy such as hot working and welding.
Alloy 718 (UNS N07718) is another precipitation hardenable nickel-base superalloy that provides very high yield strength, tensile strength, and creep rupture properties. However, the combination of properties provided by Alloy 718 degrades at very high temperatures. Therefore, the alloy is typically limited to applications that involve temperatures below about 1300° F. (704° C.).
A further precipitation hardenable nickel-base alloy designated UNS N07818 is known. That alloy has a composition that is designed to provide elevated temperature mechanical properties and processing characteristics that are intermediate to those provided by Waspaloy and 718. It has been determined that UNS N07818 can exhibit increased notch sensitivity during stress rupture testing at 1300° F. (704° C.) at higher stress levels of about 90 to 100 ksi. Notch sensitivity has been defined as the extent to which the sensitivity of a material to fracture is increased by the presence of a stress concentration area, such as notch, crack, or a scratch on the material. Higher notch sensitivity is usually associated with brittle materials, whereas lower notch sensitivity is usually associated with ductile materials. ASM Materials Engineering Dictionary, p. 294, ASM International 1992.
In view of the foregoing, it appears that there is a need for a precipitation hardenable, nickel-base alloy that provides the elevated temperature mechanical properties of UNS N07818, but with improved notch ductility at stress levels of 90 ksi and above.